. The major research focus of the OAIC is on the reduction of physical frailty resulting in a decrease in the risk of loss of independence and nursing home admission. The overall goals of this intervention study, IS-2, are to determine: whether 9 months of hormone replacement therapy (HRT) can bring about a reduction in frailty in physically frail women over 78 years of age; and whether exercise training results in greater improvements in functional capacity as reflected in strength, flexibility, balance, coordination, reaction time, aerobic power, and instrumental activities of daily living (IADL) and advanced ADL (AADL), as well as in muscle mass, cardiovascular function, and bone quantity and quality, in women who have been on HRT than in sex hormone-deficient women. Exercise training will begin after the women have been on HRT for 9 months, and will have three phases, consisting of 3 months of physical therapy exercises, 3 months of weight lifting superimposed on physical therapy exercises, and 3 months of aerobic exercise superimposed on physical therapy and weight lifting exercises. The first goal of IS-2 is to determine whether HRT can reduce frailty. The aims relative to this goal are to determine whether HRT can: a) increase skeletal muscle strength; b) increase capacity for aerobic exercise and improve cardiovascular function; c) increase bone quantity and quality; d) improve cognitive function and central processing speed; e) improve reaction time, balance, coordination, flexibility, and ability to perform IADL and AADL; f) decrease insulin resistance and improve glucose tolerance and plasma lipid and lipoprotein levels; and g) improve quality of life. Relative to the second goal, which is to determine if women who have adapted to 9 months of HRT have an enhanced adaptive response to the exercise program, the investigators will compare the magnitude of the adaptations to exercise plus HRT with the effect of HRT alone and with the effect of exercise alone in the women in IS-1. The specific aims relative to this goal are to determine whether HRT plus exercise is more effective than the exercise program alone or HRT alone in improving: a) flexibility, gait, balance, and coordination; b) strength of all major muscle groups, whole body and skeletal muscle protein anabolism, and muscle mass; c) oxygen uptake capacity; d) arterial elasticity; e) blood pressure in those with mild hypertension; f) bone mineral density in the proximal femur, spine, and other regions of the skeleton; g) cognitive function and central processing speed; and h) candidate of life. The plan is also to investigate mechanisms underlying any improvements in oxygen uptake capacity, muscle strength, blood pressure, and bone mass. Before discharge from the study, participants will be encouraged to continue HRT if there are no contraindications, and will be given individualized exercise prescriptions to follow at home. They will be helped to put together home gyms or referred to a convenient exercise facility. The investigative group will stay in contact with the graduates by means of monthly phone calls, and will bring them back to our exercise facility once per month for a training session and periodic evaluations of functional capacity using simple measures such as the standardized Physical Performance Test. Cost effectiveness and cost-utility analysis will be used to evaluate the relative costs and benefits of HRT and exercise.